Missing blenny

[Lampshade]

I had that happen to a Hawkfish of mine. Made it into the overflow. I'd checked the filter bag many times thinking he may have made it in there, it wasn't until i'd turned on and off the pump a couple time's I flushed him out of the hose... still alive. Good luck, fish can get anywhere :S. I've seen many story of fish falling behind the tank on here, hope you fair better than that.